The importance of non-quasigeostrophic forcing during the development of a blocking anticyclone

Non-quasigeostrophic (NQG) processes present prior to and during the development of a blocking anticyclone over the southern tip of Greenland on 21 January 1979 are diagnosed by comparing energy quantities and height tendencies determined from quasigeostrophic (QG) estimates with the same quantities obtained from more general formulations. Calculations were done using GLA FGGE Level III-b analyses on a 4° lat by 5° long grid. Energetics results indicate that NQG processes strengthened the intensity of the block and a precursor explosive cyclone and that a portion of this increase resulted from enhanced baroclinic conversion of eddy potential to eddy kinetic energy and reduced barotropic energy conversion from eddy to zonal flow. The height tendency fields show that the QG calculations, which generally yielded height changes that were larger than the more general height tendency model, produced smaller height changes associated with the northward amplification of the ridge from which the block ultimately formed. Further, these smaller values were primarily due to the QG vorticity advection. This suggests that NQG vorticity advection, which usually acted to moderate the wave developments, enhanced the block development. In fact, it is suggested that QG forcing might not have been adequate to produce the observed block development. Non-quasigeostrophic processes were also significant in the static stability advection term but were of little consequence in the differential thermal advection.